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DJDRAW -BAUGH. TELEPHONE TRANSMITTER;

No. 295,742. Patented Mar. 25,1 84.

" INVENTOR ,9 ITNESSES I Yr d-fl n Q A.) ATTORNEY;

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UNITED STATES PATENT "O FICE.

DANIEL DRAWBAUGH, or EBERLYS MILL, PENNSYLVANIA, ASSIGNOR TO,

THE rnornn s TELEPHONE COMPANY, on NEW YORK.

TELEPHONE-TRANSMITTER.

SPECIFICATION forming part of Letters Patent No. 295,742, datedlVLarch25, 1884.

Applicationfiled November 19, 1883. (No model.)

T0 at whom it may concern:

Be it known that I, DANIEL DRAWBAUGH, of Eberlys Mill, Cumberlandcounty, Pennsylvania, have invented a new and useful Improvement inTelephone-Transmitters, of

. of a suitable substance in pulverized form,

mixed with a binding material, to produce a plastic or semi-liquid masscapable on drying of hardening. I have found it to be quite sufficientfor all practical purposes to apply a thin coating or layer of thiscompound over the surfaces of any pieces of conducting material,

is the box or case.

and then, when said coating is hardened, to place the two surfaces incontact and in circuit. l

Referring to the drawings, Figure l is a front view of atelephone-instrument in which my invention is embodied, one of thediaphragms in saidflinstrument being removed. Fig. 2 is a verticalsection on the line as 00. Fig. 3 is a face view of one of theconductingplates coated partially with my electrode compound. Fig.plates coated with the electrode compound and placed in contact,substantially as in the instrument. Fig. 5 is a rear view of the frontdiaphragm. i

Similar letters indicate like parts.

.A is the back board of the instrument; B

O is the front cover, having a moutlrorifice. D is the rear cover, alsohaving a central orifice. E is the front diaphragm. F is the reardiaphragm. G G are blocks of wood or other material, supporting theinstrument'at a distance from the back board, A. By this constructionsound-waves impinge upon the diaphragm E directly, and upon thediaphragm F after reflection from the back board, A, thus vibrating bothdiaphragms relatively in opposite directions simultaneously. Theelectrodes are arranged between the two diaphragms, one electrode beingfixed to the rear diaphragm, and having an inclined upper surface, andthe other one resting upon said inclined surface by grav- 4 shows twoconducting ity, and receiving motion from the front diaphragm, E. Thisgeneral construction of instrumentthat is to say, with two diaphragmsand two electrodes arranged between them has already been fully setforth by me in other applications, and therefore is not hereinspecifically claimed.

To therear diaphragm, F, and at about its center, I secure a block ofwood or other suitable material, H, upon which I attach by a screw, asshown in Fig. I, or in any other convenient way, a metal plate, I. Thisplate is covered or coated with what I have already designated as myelectrode compound, which I may prepare in the following way: Ipulverize gascarbon finely and mix it with what is known asrubber-varnish that is to say, pure rub ber dissolved in bisulphide of.carbon-so as to form a pasty mass, which I prefer should not be so thickas to prevent its flowing from the brush. I do not limit myself to anyparticular consistence of this mixture, because it maybe desirable insome cases to haveitthick or viscid and in others thin and flowing. I'

have found, however, that it is more convenient to make the compound notmuch thicker than ordinary varnish, so that it can be applied easilywith the brush.

I do not limit myself to any particular binding material--such asrubbervarnish-because I may use other agglutinating mixtures in placethereofsuch, for example, as shellac dissolved in alcohol, or evenordinary glue, or copal-varnish, or Chinese Japan varnish. All of thesesubstances give good results; but I think, in practice, it is best touseamaterial which does not absorb moisture, as does glue, and whichwill cause the compound to dry and harden quickly through theevaporation of a volatile-constituent-such, for example, as alcohol orbisulphide of carbon.

Referring now to the drawings, Fig. 3 shows the metal plate I partiallycovered with the electrode compound. The plate may be wholly covered 5but I think the results are a little better when it is partiallycovered, substantially as here shown.

J is another metal plate covered with my electrode compound usedsubstantially the same way. To the back of this plate. is so cured aprojecting piece, L, also of metal,

having a curved outer edge. On the diaphragm E, I secure'two pieces ofwood, M, With a space between them, into which space enters the curvededge of the projecting piece L, as shown in Fig. 2. These pieces Mprevent lateral displacement of the upper electrode, J L, which restsupon the lower electrode by gravity. I find it preferable to make theangle of inclination of the electrode I about forty-five degrees.

The circuits in the instrument proceed as follows: from the battery tothe binding-post 1, by the wire a, to the induction-coil N, through theprimary of said coil, by the wire b, to the plate I, through layers ofelectrode compound to .the plate J, projection L, and thence by the wire0, connected to said projection, and to the contact-plate P, thence tothe spring and contact-plate Q, and thence by the wire 01 to thebinding-post 2, and back to the battery. The secondary coil of theinduction coil N connects, by wires 6 e, to the-line binding-posts 3 and4, and from said wires 6 e branch wires f f extend to the binding-posts2 5 5 and 6, to which a receiving-instrument may be attached. The springcontact-piece Q overlaps the plate P, and has a rectangular downwardprojection, so that when the ring of a receiving-instrument is placedover the arm B, said contact-plate Q, is raised and the circuit betweenthe parts P and Q is broken.

S is 'a bar for holding the induction-coil M in place. Saidinductioncoil passes through an opening in the rear diaphragm, F, and issecured to the back board, A. The vibrations of the diaphragms arecommunicated to the electrodes, so that the latter cause modificationsof the current passing through them.

I do not limit myself to two electrodes provided with a coating offinely-divided conducting material mixed with an agglutinatingsubstance, inasmuch as I have used one electrode consisting of a plateof metal or other conducting material combined with a second electrodecoated as described. The plates coated may be either of conducting ornon-conducting material. In thelatter case electrical circuit-connectionis established directly with the coating.

I claim as my invention- 1. In a telephone-transmitter, electrodesconsisting of flat plates having their surfaces in contact, the saidsurfaces beingcovered with a hard, thin coating of finely-dividedconductof a thin stratum of finely-divided conducting material, combinedwith an agglutinatin g substance, substantially as described.

3. A telephone electrode or resistance-varying conductor fortelephone-transmitters, consisting of a plate covered with ahard, thincoating of finely-divided conducting material, combined with anagglutinating substance, substantially as described.

' 4- In a telephone-transmitter, electrodes consisting of metallicplates or surfaces provided with a hard,thin coating of finely-dividedconducting material, combined with an agglutinating substance, the saidcoated surfaces being in contact, substantially as described.

5. In a telephone-transmitter, electrodes consisting of metallic plateshaving their surfaces partially covered with a hard, thin coating offinely-divided conducting material, combined with an agglutinatingsubstance, the coated portions of said plates being in contact,substantially as described.

6. In a telephone-transmitter, and rigidly attached to a support, aninclined plate or surface coated with a mixture of finely-dividedmaterial and agglutinating substance, in combination with a movableplate similarly coated and pressing by gravity upon said inclifiedsurface, and a diaphragm acting upon said movable plate, substantiallyas described.

7. In a telephone-transmitter, the combination of the diaphragm E,guides M, plate J, coated with a mixture of finely-divided conductingmaterial and agglutinating substance, and having a projection, L7similarly coated plate, I, and an inclined support for said plate I,substantially as described. 7

8. In a telephone, the combination, with the diaphragm and the fixedsupport carrying the inclined electrode, of the loose plate having asurface of conducting material resting upon the fixed electrode, and aprojection in contact with the diaphragm, substantially as described.

DANIEL DRAVVBAUGH,

Witnesses:

FRED. M. OTT, M. W. JACOBS.

